Regression of increases in total daily energy expenditure (MJ/day) and state 4 respiration (pmol O₂/(s·mg muscle·CS activity)) (p<0.02, R² = 0.50).

<p>Regression of increases in total daily energy expenditure (MJ/day) and state 4 respiration (pmol O₂/(s·mg muscle·CS activity)) (p<0.02, R² = 0.50).</p

Baseline and mild cold values of a) total daily energy expenditure, b) activity, c) state 4 respiration, and d) state 3 respiration.

<p>The figures show mean (±SEM) in both situations. * p<0.05, ** p<0.01</p

Study protocol.

<p>The thermoneutral experiment started in the morning on day one. After one hour a blood sample was taken and subsequently the [¹⁸F]FDG tracer was injected followed by the PET-CT scan one hour later. In the afternoon of day one, the shivering experiment was conducted, which started with a baseline period of 45 minutes during 31°C followed by 90 minutes of mild cold exposure (31°C) to determine the ambient temperature at which shivering occurred. The mild cold experiment on day two consisted of 45 minutes baseline (31°C) followed by 150 minutes of cold exposure. Blood samples were taken at the end of the baseline period and 90 and 150 minutes after the onset of cold exposure. The [¹⁸F]FDG tracer was injected 90 minutes after the onset of cold exposure, followed by the PET-CT scan one hour later.</p

Frequent Extreme Cold Exposure and Brown Fat and Cold-Induced Thermogenesis: A Study in a Monozygotic Twin

<div><p>Introduction</p><p>Mild cold acclimation is known to increase brown adipose tissue (BAT) activity and cold-induced thermogenesis (CIT) in humans. We here tested the effect of a lifestyle with frequent exposure to extreme cold on BAT and CIT in a Dutch man known as ‘the Iceman’, who has multiple world records in withstanding extreme cold challenges. Furthermore, his monozygotic twin brother who has a ‘normal’ sedentary lifestyle without extreme cold exposures was measured.</p><p>Methods</p><p>The Iceman (subject A) and his brother (subject B) were studied during mild cold (13°C) and thermoneutral conditions (31°C). Measurements included BAT activity and respiratory muscle activity by [¹⁸F]FDG-PET/CT imaging and energy expenditure through indirect calorimetry. In addition, body temperatures, cardiovascular parameters, skin perfusion, and thermal sensation and comfort were measured. Finally, we determined polymorphisms for uncoupling protein-1 and β3-adrenergic receptor.</p><p>Results</p><p>Subjects had comparable BAT activity (A: 1144 SUV_total and B: 1325 SUV_total), within the range previously observed in young adult men. They were genotyped with the polymorphism for uncoupling protein-1 (G/G). CIT was relatively high (A: 40.1% and B: 41.9%), but unlike during our previous cold exposure tests in young adult men, here both subjects practiced a g-Tummo like breathing technique, which involves vigorous respiratory muscle activity. This was confirmed by high [¹⁸F]FDG-uptake in respiratory muscle.</p><p>Conclusion</p><p>No significant differences were found between the two subjects, indicating that a lifestyle with frequent exposures to extreme cold does not seem to affect BAT activity and CIT. In both subjects, BAT was not higher compared to earlier observations, whereas CIT was very high, suggesting that g-Tummo like breathing during cold exposure may cause additional heat production by vigorous isometric respiratory muscle contraction. The results must be interpreted with caution given the low subject number and the fact that both participants practised the g-Tummo like breathing technique.</p></div

Brown adipose tissue and respiratory muscle activity during the thermoneutral and cold exposure experiment. A, D

<p>) PET images during thermoneutral (left) and cold (right) conditions showing [¹⁸F]FDG-uptake e in brown adipose tissue (BAT; red arrows) and respiratory muscles (RM; white arrows). <b>B, E</b>) Transaxial slices of subject A (5 mm thick) of thoracic area (upper) and supraclavicular area (lower) demonstrating BAT activity (red arrows) and RM activity (white arrows). <b>C, F</b>) [¹⁸F]FDG-uptake (SUV_mean) in BAT, white adipose tissue (WAT), skeletal muscle (SM), and respiratory muscles (RM) during thermoneutral and cold conditions.</p

Metabolic, cardiovascular and thermoregulatory parameters during mild-cold experiment.

<p>Metabolic, cardiovascular and thermoregulatory parameters during mild-cold experiment.</p

PET-images of fifteen morbidly obese subjects.

<p>Three female subjects showed BAT activity in the supraclavicular area, highlighted by a red rectangle (A). Combined PET- and CT-imaging shows FDG-uptake in supraclavicular adipose tissue (this was the morbidly obese subject that showed the most BAT activity) (B).</p

Subject characteristics.

<p>*<i>WI  =  work index, SI  =  sport index, LI  =  leisure time index</i>,</p

Energy expenditure, body core temperature, mean skin temperature and core-skin temperature gradient in thermoneutral conditions (TN) and during mild cold (Cold) in morbidly obese subjects.

<p>Energy expenditure, body core temperature, mean skin temperature and core-skin temperature gradient in thermoneutral conditions (TN) and during mild cold (Cold) in morbidly obese subjects.</p

Brown adipose tissue activity in relation to body mass index (A) and body fat percentage (B).

<p>The black dots indicate the current study group, the open dots indicate previously performed measurements. Cold-induced thermogenesis (CIT), denoted in percentages, is significantly increased in 26 BAT-positive (BAT+) compared to 13 BAT-negative (BAT-) subjects (C). *: P<0.05.</p